Academic Script 1.Introduction Do you know that the Reptiles dominated our planet for a long time? Animals of Class Reptilia, first appeared in late Paleozoic and they became numerous by Mesozoic. This is known as “The Age of Reptiles"
These are the first Vertebrates completely adapted for life on land, though a few have become secondarily aquatic.
We will study the characters and position of Reptilia by studying the classification of the living reptiles in the first part on Reptiles.
Reptiles are distinguished by the characters like:
1. Reptiles are ectothermal, sometimes called heliotherms because they can regulate body temperature by using solar radiation, terrestrial or aquatic Tetrapoda.
2. Generally they have an exoskeleton of dry epidermal scales, bony plates or scutes.
3. Endoskeleton is more completely bony than in Amphibians.
4. The skull has one occipital condyle,
5. Vertebral column is differentiated into regions,
vertebrae are gastrocentrous,
and in living forms two vertebrae form a sacrum,
ilio-sacral articulation is postacetabular.
6. The limbs are short, pentadactyle and ending in horny claws.
7. The locomotion is generally by creeping hence they are called Reptilia = reper to creep
8. Lungs are the sole respiratory organs, except in some aquatic Chenolia in which cloaca is respiratory.
9. The heart is imperfectly four-chambered showing two auricles and incompletely divided ventricle. Or totally divided in Crocodilians
10. Kidneys are metanephric with no nephrostomes and
12. There is a cloaca which is often complicated.
13. Fertilization is internal because male has single or double penis as external copulatory organs.
14. The egg is provided with two characteristic membranes called amnion and allantois.
The amnion serves as a private aquarium to prevent the egg from desiccation
Allantois serves as embryonic respiratory and excretory organ,
A yolk sac provides nourishment.
15. Reptiles are the first true Vertebrates because the cleidoic i.e. closed / self-contained egg which is laid and develops on land,
Even aquatic Reptiles come on land to lay eggs.
No metamorphosis is seen.
2.Position of Reptiles in Animal Classification Now let’s see the Position of Reptiles in the Animal Classification:
Kingdom - Eukaryota
Subkingdom - Metazoa
Division - Eumetazoa
Phylum - Chordata
Subphylum - Vertebrata
Group - Gnathostomata
Superclass - Tetrapoda
Clade - Amniota
(Laurenti stated 1768 Subgroups) Class Reptilia is further classified into 6 Subclasses: 1. Anapsida
6. Synapsida Here Anapsida, Lapidosauria and Archosauria consist of living Reptiles.
Reptiles (Reptilia) are a diverse group of Vertebrates that includes creatures such as Snakes, Amphisbaenians, Lizards, Alligators, Caimans, Crocodiles, Tortoises, Turtles, and Tuataras.
There are approximately 7900 species of Reptiles alive today that inhabit a wide range of temperate and tropical habitats including deserts, forests, freshwater, wetlands, mangroves and Open Ocean.
Reptiles are cold-blooded vertebrates which, unlike Amphibians, possess thick, impermeable skin covered by scales. The Reptilian skeleton differs from other Vertebrates in various ways. For example, Mammals have a single lower jawbone called the mandible but Reptiles have several bones in their lower jaw that enable them with greater bite mobility.
Also, Reptiles have only one bone in each ear (the stapes) whereas Mammals have three small bones in each ear (the malleus, incus and stapes). Reptiles also have only one occipital condyle, a protrusion on the skull that forms a joint that enables movement of the head, while Mammals and Amphibians have two occipital condyles. They have lungs, not gills, and usually a three-chambered heart, except for Crocodilians, whose hearts have four chambers. Their eggs are covered with watertight shells; thus they have severed the Amphibians link to water and fully conquered land. Described living species are 7,131.
Order 1: Chelonia. Permian to Recent Turtles are distinguished by their large shells, which consist of an outer carapace and a breast-covering plastron. They live throughout the world, in the ocean, in fresh water, and on land in which case they are called Tortoises. Some Turtles are believed to live for more than 150 years. Only distantly related to other living Reptiles, turtles have changed little in the last 300 million years. Described living species are 260.
We can describe them as:
They are terrestrial or aquatic
Tetrapoda pentadactyle with walking limbs or paddles.
Trunk is enclosed in a bony shell-dorsal carapace and ventral plastron, which may or may not be covered with horny shield.
Tail is always present.
Jaws covered with horny epidermal plates, no teeth.
Quadrate bone is fixed.
Thoracic vertebrae and ribs modified along with epidermal plates usually fused to form the shell.
Two sacral vertebrae.
Ribs with capitulars portion only.
Girdles inside the ribs
Humerus with entepicondylar foramen.
Pubis and Ischia form symphysis.
Copulatory organ is unpaired.
Cloacal opening is longitudinal.
Little change since Triassic and are the oldest living reptile in the world.
Examples: Chelus, Emys, Chelonia, Testudo. 4. Sub-class 2: Lepidosauria Subclass 2 Lepidosauria (Scaly Lizards): The main feature of the period of Reptilian dominance, the Diapsid skull is found in these animals and which is present in all living Reptiles except the Chelonia and in the birds. The Lepidosauria which includes Sphenodon, the Lizards and Snakes. They show the characteristics like:
Two temporal vacuities are present.
Anterior orbital vacuities are absent.
Post-temporal fenestrae are usually present.
Humerus with two foramina.
Order 1: Rhynchocephalia : Triassic to Recent. Only two species remain of this ancient line of Lizard-like Reptiles, which now live only in certain parts of New Zealand. They possess:
The presence of Two vacuities.
An epipterygoid is present.
Quadrate bone is fixed or immovable.
Parietal foramen is present.
External copulatory organs are entirely absent.
Order 2: Squamata: Triassic – Recent
Body covered with horny epidermal scales.
Single (supra or upper) temporal vacuity in Lizards and no temporal vacuity in Snakes.
Skull has lost one or both temporal regions
Teeth set in sockets- pleurodont.
Quadrate is movable.
Vertebrae are usually procoelous.
Abdominal ribs usually greatly reduced or absent
Limbs present or absent.
Cloacal opening transverse.
Male possesses a pair of eversible copulatory organs.
Contains most modern reptiles.
There are three groups of Reptiles evolved comparatively recently means in the Jurassic period, so that even today they share certain anatomical similarities and are all put in the same order.
Examples: Snakes (known from Cenozoic), Lizards (from Cretaceous) and Amphisbaenians (from Eocene). Described living species are 6,847.
Suborder 1: Lacertilia ,Triassic to Recent The most successful of all the Reptiles, Lizards represent about 54% of Reptilian species. Extremely diverse as well, Lizards live on every continent except Antarctica, and in nearly every conceivable habitat, from deserts to tundras, mountains to oceans
Terrestrial, arboreal or burrowing forms have slender body.
Single (supra or upper) temporal vacuity is present.
Limbs are usually present Tetrapoda and Pentadactyle
The rami of mandibles are fused in front.
Familiar examples include Chameleons, Iguanas, Geckos, Skinks, Monitor Lizards & many more.
Examples: Lacerta, Scincus
Infraorder 4: Anguimorpha. Cretaceous to Recent
Examples: Varanus, Anguis
Suborder 2: Ophidia: Cretaceous to Recent Snakes: Of all the tetra pods that have lost their limbs (including Caecilians, Sirens, Worm-lizards, and a variety of Lizards), Snakes are by far the most successful. They are exclusively carnivores, and often-fearsome predators. Their muscles have adapted for swift movement; their digestive systems allow them swallow the whole prey and their bodies have adapted to an extremely wide range of environments. They live on every continent except Antarctica. Described living species are 2647.
Terrestrial or aquatic, arboreal or burrowing.
Temporal vacuities are entirely absent.
The rami of mandibles are united by a ligament.
Tongue is bifid or protrusible.
Zygosphene and zygantra are present in the vertebra.
Examples: Python, Natrix, Naja, Vipera Suborder 3: Amphisbaeniaor Worm lizards: Recent They are unique. Not only are they limbless, like Snakes; they are also, among living Reptiles, the only specialized burrowers, and live exclusively underground. They inhabit inSouth America, Africa, Spain, and the Middle East. Described living species are 133.
5. Sub-class 3: Archosauria Subclass 3: Archosauria -The Ruling Reptiles They were the dominant land animals during Mesozoic. Crocodiles are the only descendants of this group. The Birds, which are also undoubtedly descendants of this group, give us in some ways a better idea of characteristic structure.
Skull with closed upper temporal vacuity but possesses both temporal arches means Diapsid skull.
Anterior orbital vacuities are usually present.
Teeth are thecodont.
Humerus with foramina
Vertebrae are amphicoelous or procoelous.
Some lines had the tendency to walk on the hind legs like Dinosaurs and Pterosaurs where the hind legs were much longer.
Order 1: Crocodilia: Triassicto Recent
They are fresh water or predatory forms.
Body is covered with an exoskeleton of thick horny epidermal scales.
Bony plates embedded in epidermis
Tail is long and laterally compressed.
Maxillae, palatines and pterygoids are united along the middle to form a secondary palate.
Teeth set in sockets-thecodont.
Quadrate immovable- fixed.
Both supra and infra arches are present.
Sternum is present.
Cervical vertebrae with two headed ribs.
Thoracic ribs possess uncinate process.
Abdominal ribs present in Gastralia
Prepubis present. Pubis does not share in the formation of acetabulum.
Heart is four chambered and Ventricles completely separated into two septum.
Lungs are spongy.
Cloacal opening longitudinal.
"Crop" similar to birds.
Examples: Crocodylus, Alligator, Caiman, Gavialis
6.Poisonous Snakes & Treatment on snake bite Poisonous Snakes of India: There are about 300 varieties of Snakes out of which only 30 are Poisonous.
Before knowing about Poisonous & Non-poisonous Snakes let’s have some Awareness of the Primary Treatment on the Snakebite. Ayurveda, the basic Indian medication suggests many solutions to face the problems of different types of snakebites applied since centuries.
Wherever the Snake bites, First of all tie up that organ tightly from 4 inch far of the bite towards the heart side. Due to which the poison will not spread all over the body.
The Neem tree – Azadirecta indica: A plant of Indian origin is very useful for more than 30 diseases.Here a simple process to follow for snakebite:
The patient has to eat leaves of neem tree. if poison has been mixed into the blood, the bitter taste will not be felt.
The permanent solution for safety one has to eat few leaves of the Neem tree daily, which will give permanent immunity from the Snake Poison.
The paste of Neem leaves is also effective to neutralize the effect of Snake Poison. This paste can be used orally andapplied locally too.
Give the paste of the roots ofCarissa (Karamdi) orally with water to the patient of Snakebite and watch. If the patient doesn’t start vomiting it shows that the poison has been mixed in the blood & if he starts vomiting means he is out of danger.
The soapy water of Sapindus trifoliate (Ritha plant) is to be applied in the eyes of the patient, if the eyes start burning it shows that there is no poisonous effect. But if it is there, go on applying this water to the eyes. Whenever the effect of poison is neutralized the patient will start complaining about burning sensation
A polyvalentserum that effectively neutralizes the venom of all of the Big Four Snakes is widely available in India and is frequently used to save lives.
Remember that mostly people die due to the fear of snakebite & not by the poison of it.
Key to identify poisonous or non-poisonous snakes:
1. Sea snake:
Tail laterally compressed.
Head scales large.
2. Russel’s viper:
Belly scales broad.
Thick trunk and Short tail.
Three rows of diamond-shaped marks on back
3. Pitless viper:
Belly scales broad.
White, arrow- shaped mark on head.
Head scales small.
Scales below tail entire. i .e. subdivided.
4. Pit viper:
Belly scales broad.
Head scales large.
A pit between nostril and eye.
Belly scales broad.
Mid-dorsal scales large.
4th lower labial largest.
Scales below tail entire.
Belly scales broad.
Head scales large.
Expanded hood, marked by ‘V’.
3rd labial touching eye and nostril.
Indian cobra, Naja naja, probably the most famous of all Indian snakes.
Common krait, (Bungarus caeruleus), Russell's viper, (Daboia russelii), Sind Saw-scaled viper, (Echis carinatus). are the venomous snake species responsible for causing the most snake bite cases in South Asia, mostly in India.
Whenever you see the Snake try to identify and never be panic. If the snake is very nearer don’t move till it passes, but if you try to harm the snake, it may harm you.
To understand the distinguishing characters of the Reptiles as the First land Vertebrates
To have understanding about the position of Reptilia in the Animal Kingdom and how they are classified
To understand the classification of living Reptiles by their characters
To have simple awareness for the treatment against snakebite
To have a clear understanding of the Poisonous & Non-poisonous Snakes
Frequently Asked Questions Q1. How many recognized species of Reptiles are there on the planet?
Which are the main orders of Reptiles?
A1. According to the EMBL Reptile Database, as of June 2005 there are approximately 8,240 recognized species of Reptiles on the planet. They are divided into four distinct orders.
1. The CROCODYLIA which comprise 23 living species.
2. The CHELONIA (Turtles) which comprises 307 species. Finally we have the RHYNCOCEPHALIA which is New Zealand’s Tuatara. There are only 2 living species.
3. The SQUAMATA which is subdivided into the
(a) LACERTILIA or Lizards at about 4,765 species,
(b) The AMPHISBAENIA or worm Lizards at about 165 species
4. The SERPENTES which are the Snakes. They comprise 2,978 species.
The Reptilia are the third largest class of vertebrate. For perspective, compare them to mammalia, of which there is only around 4,629 recognized species.
Q2. Is there a difference between a Herptile and a Reptile?
A2. This is a rather strange word; Herptile. The name is meant to include the Reptiles and the Amphibians in the same category. But as we have studied many distinguished characters of Reptiles, they can’t be placed with Amphibians. Since Reptiles and Birds would be better to classify together as they have more in common.
Q3. What is the difference between an Amphibian and a Reptile?
A3. There are the 3 main differences :
1. Amphibians have smooth skin, Reptiles have scales.
2. Amphibians need the water. There are also Amphibians that are able to spend their whole lives out of the water. While reptiles are total land animals, yet this is not always true. There are many marine Reptiles, but they must go ashore to lay their eggs. Sea snake might be a possible exception.
3. All Amphibians have soft jellylike eggs. Reptiles use hard shelled amniotic eggs.
Q4. Can Turtles come out of their shells?
A4. No, only cartoon Turtles can come out of their shells. In real Turtles, the shell is a part of the body connected to the backbone and ribs. A Turtle coming out of its shell would be a very messy thing indeed. Q5. Do Snakes "sting" with their tongues?
A5. No Snake tongues are forked so that they can fit into a special smelling organ in the mouth called the Jacobson's organ. It has two pits in it, which is why a Snake's tongue is forked.
No Snake stings either. Some inject venom, via specially grooved fangs, some in the front, and others in the back.
So, Snakes can't sting with their tongues.
Quiz 1. Animals of which order have changed a little since Permian?
2. Suborder Lacertilia is classified under.........
4. Members of which Reptile group show the four chambered heart?
5. Reptiles are called first true Vertebrates because...........
A. Metamorphosis is seen.
B. The cleidoic egg is laid & develops on land.
C. They are burrowers.
D. They are Tetrapoda, hence easily move on land.
Answer Q1. Animals of which order have changed a little since Permian?
Q2. Suborder Lacertilia is classified under.........
Q3. Which of the following animals possesses the presence of sternum, movable eyelids and tympanum?
A3.Varanus. Q4. Members of which Reptile group show the four chambered heart?
Q5. Reptiles are called first true Vertebrates because...........
A5. The cleidoic egg is laid & develops on land.
Summary Reptiles dominated our land for many centuries. This module covers the characteristics of reptiles and gives details of three living subclasses of reptiles, namely, Anapsida, Lepidosauria and Archosauria. It also describes the poisonous snakes and treatment on snakebite.
Tutorials: This topic does not contain any tutorials.
Go to a zoo & try to identify the snakes whether they are Poisonous or Non-poisonous.
Visit a museum where fossils of Dinosaurs are available & imagine about the Golden era of Reptiles, you will really enjoy it.
If you ever have trouble telling a Salamander apart from an Alligator Lizard then you can try looking for eggs, but if there aren't any around then just feel the skin, but be careful, amphibians are also known to have toxic secretions on their skin (something most Reptiles lack)
Books The Life of Vertebrates - J. Z. Young, Emeritus Professor of Anatomy, University college, London - Third Indian Edition, Oxford University Press
Chordate Zoology & Animal Physiology, Lucknow Christian College, Lucknow - E.L. Jordan, P.S. Verma , Department of Zoology, Meerut college, Meerut.
Animal Classification - D. K. Apsangikar.
Aryabhishak or Hindustan no Vaidyaraj – An Ayurvedic book, 11th Edition printed in 1951. - Lt. Ayurved Martand Shastri Shankar Daji Pade - Translation in Gujarati by Harikrushna Bhagvanlal Vyas, - Sastu Sahitya Vardhak Karyalaya, Mumbai.
Note: In this book a list of 700 reference books is also given. Before this edition more than 50,000 copies were sold. Later more editions are also published, which shows that how Ayurved is woven in Indian culture. Links: